Electric power transmission and distribution commonly relies upon cables strung overhead. Overhead conductor cables are commonly suspended from messenger cables which are typically made of high strength alloys. Messenger cables are supported on poles or towers and support conductor cable spacers arranged at spaced intervals along the messenger cable. In practice, a single spacer is used to support all three low voltage conductor cables in a three-phase system and the spacer simultaneously maintains a spaced relation between each of the conductor cables. Prior art spacers have been attached to the messenger cable and to the conductor cables in order to save space and to maintain appropriate distances between suspended conductor cables.
U.S. Pat. No. 4,020,277 issued Apr. 26, 1977 to Hendrix Wire & Cable Corporation discloses a spacer for aerial cables. The disclosed spacer includes a body member having at least one generally arcuate cable-retaining means adapted to engage a surface of the conductor cable and retain the cable in a concave seat of the spacer. One end of the cable-retaining means is pivotally supported on the body member. Generally arcuate ratchet tooth means are provided adjacent the other end of the cable-retaining means and arcuate ratchet tooth means are provided on the body member outwardly of the concave seat. The teeth of the retainer ratchet tooth means engage with the teeth of the body member ratchet tooth means when the retaining means is rotated about its pivotal support, thereby firmly retaining the conductor cable in the concave seat.
Since many power circuits require three phase electric power, it is often convenient to suspend conductor cables in groups of three using spacers. However, it has been found that the prior art spacers are not satisfactory for high voltage conductor cables, i.e., voltage at or above 50 kV, e.g., 69 kV, 115 kV or 138 kV (phase to ground) used in three-phase power transmission. The voltage difference between the cables requires greater spacing than low voltage cables require, and greater voltage differences between cables require larger spacers. The larger cables, larger spacers, and larger voltage create cost problems that render prior art spacer designs unsatisfactory.
Prior art spacer systems are also incapable of retaining high voltage cables reliably in the event of certain problems with power transmission, e.g., a short circuit. When power transmission cables experience a short or arc, the cables buckle, which translates significant force to the spacers. High voltage cables generate greater force with a short than do low voltage cables and testing has shown that prior art spacers cannot handle the force of a buckling high voltage cable.
High voltage applications currently employ spacers only in direct current (DC) systems, which do not have the issue of significant voltage differences between the cables and the attendant problems thereof experienced in AC systems. High voltage AC conductor cables are typically suspended from poles without the use of spacers, in order to ensure sufficient distance between suspended cables. However, hanging cables that are oriented side-by-side in the same plane requires a wider footprint than would be required if the use of spacers were possible. Furthermore, when spacers cannot be used, poles must generally be located nearer to one another than would be the case if spacers could be used.